1. Technical Field
The present invention relates to a method for manufacturing a multilayer ceramic substrate.
2. Related Art
Low temperature co-fired ceramics technique enables a collective firing of a green sheet and metal, realizing an element mounting substrate in which various types of passive elements are built-in between ceramic layers. In terms of a mounting technique of system on package (SOP), a manufacturing method relating to the element mounting substrate (hereinafter, referred to as merely a multilayer LTCC substrate) has been devotedly developed in order to compound electronic components and minimize parasitic effect occurring at surface mounting components.
In the method for manufacturing a multilayer LTCC substrate, a drawing step, a pressure-bonding step, and a firing step are sequentially conducted. In the drawing step, patterns of passive elements and wirings are drawn on each of a plurality of green sheets. In the pressure-bonding step, the plurality of green sheets having the patterns are laminated to be pressure-bonded. In the firing step, a pressure-bonded body obtained through the pressure-bonding step is fired at a time.
For the drawing step, JP-A-2005-57139, as a first example, discloses an ink-jet method in which a conductive ink is discharged as fine droplets so as to densify various patterns. According to the ink-jet method, patterns are drawn with droplets of several picoliters or several dozen picoliters. Therefore, changing of discharging positions of the droplets can realize miniaturization of patterns or pitch narrowing.
For the pressure-bonding step, JP-A-5-315184, JP-A-6-77658, and JP-A-2007-201245, as a second to fourth examples, disclose a hydrostatic pressure method by which hydrostatic pressure is applied to a laminated body in order to stabilize a laminating state of green sheets. The hydrostatic pressure method decompress-packages the laminated body and then leaves it in a heated liquid so as to increase static pressure of the liquid. Accordingly, pressure can be uniformly applied to the laminated body.
FIGS. 14A to 17B show a shape of a pattern in the drawing step and the pressure-bonding step described above. FIG. 14A is a plan view illustrating a shape of a pattern in the drawing step, and FIG. 14B is a sectional view taken along the line 14-14 of FIG. 14A. FIG. 15A is a plan view illustrating a shape of the pattern, which is shown in FIGS. 14A and 14B, in the pressure-bonding step, and FIG. 15B is a sectional view taken along the line 15-16 of FIG. 15A.
FIG. 16A is a plan view illustrating a shape of a pattern with another pattern that is laminated, in the drawing step, and FIG. 16B is a sectional view taken along the line 16-16 of FIG. 16A. FIG. 17A is a plan view illustrating a shape of the pattern, which is shown in FIGS. 16A and 16B, in the pressure-bonding step, and FIG. 17B is a sectional view taken along the line 17-17 of FIG. 17A.
A conductive ink used in the ink-jet method in the drawing step is a dispersal system of conductive fine particles of which a particle diameter is commonly several nanometers to several dozen nanometers. As shown in FIGS. 14A to 16B, a pattern 101 formed through the drawing step is an aggregate of conductive fine particles 102, so that even if a solvent or a dispersion medium is evaporated, the pattern 101 keeps to have high fluidity until it is fired in the firing step.
In the pressure-bonding step, as shown in FIGS. 15A and 15B, for example, green sheets 103 sandwiching the pattern 101 are pressure-bonded by atmospheric pressure. At this time, the conductive fine particles 102 before fired are easily squashed by the atmospheric pressure in the decompress-packaging because the conductive fine particles 102 have weak adherence with respect to the green sheets 103 and weak binding power with each other. As a result, the pattern 101 deforms to extend along a main face 103a of the green sheets 103, overflowing from a desired pattern region 104 (two dot chain line in FIGS. 14A to 15B). Therefore, patterns 101 that are adjacent each other are electrically connected disadvantageously.
Further, as shown in FIGS. 16A and 16B, if the green sheets 103 are laminated so as to form a laminated body, a portion of patterns 101 (the conductive fine particles 102) of the green sheet 103 positioned upper and a portion of patterns 101 of the green sheet 103 positioned lower are overlapped with each other in a laminating direction. The portions, which are overlapped with each other, of the patterns 101 of the green sheets 103 in the laminated body are largely affected by pressing force when the laminated body is pressed from up and down direction, compared to other portions of the patterns 101. Therefore, as shown in FIGS. 17A and 17B, the portions, which are overlapped in a laminating direction, of the patterns 101 largely deform compared to the portions, which are not overlapped in the laminating direction, of the patterns 101, overflowing from a desired pattern region 104 (shown by two dot chain line in FIGS. 16A to 17B). As a result, the patterns 101 overlapped with each other in the laminating direction disadvantageously further progresses the electrical connection, described above, between the patterns 101.